A costly weevil that dines on clover pastures and has extended its reach to northern parts of West Coast farmland will soon come up against more releases of a natural predator.
Increasing clover root weevil populations are being seen on the Coast and AgResearch intends to block their infestation with the release of the Irish wasp, a proven biocontrol agent against the serious pest.
Sampling last winter revealed the weevil was present through much of the northern parts of the Coast and Lincoln-based AgResearch entomologists Dr Scott Hardwick and Mark McNeill are asking southern farmers to report weevil movement so they can be sure the wasp can keep pace with the problem.
The biocontrol project began in 2006 when AgResearch scientists, supported by industry good bodies DairyNZ and Beef + Lamb NZ and research trust Agmardt, first released the tiny parasitic wasp from Ireland.
Within 18 months trial releases in Waikato, Hawke’s Bay and Manawatu had exceeded scientist expectations.
Hardwick said potentially damaging populations had been traced from Greymouth to Karamea but only a single infested site in Waitahi had been found to the south despite extensive testing.
''The good news is that clover root weevil has brought its own destruction with it. The Irish wasp has been confirmed at many localities including Little Wanganui, the outskirts of Westport, Cronadun, and Greymouth. However, we're concerned that the weevil may be getting a jump start on the wasp further south on the West Coast. In wetter areas, clover root weevil may not fly as readily as it does in summer dry areas such as Canterbury.''
The lower flight time limits the dispersal power of the Irish wasp, travelling as eggs inside parasitised weevils.
Scientists are considering carrying out releases of the Irish wasp south of Greymouth when new populations of the weevil are found rather than relying on it making its own way.
The weevils can be tracked by the distinctive U-shaped notches on clover leaves made by the adults.